U.S. patent application number 11/033281 was filed with the patent office on 2006-03-16 for apparatus and method for controlling operation of compressor.
This patent application is currently assigned to LG Electronics Inc.. Invention is credited to Chel-Woong Lee, Ji-Won Sung, Jae-Yoo Yoo.
Application Number | 20060056980 11/033281 |
Document ID | / |
Family ID | 36157400 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060056980 |
Kind Code |
A1 |
Yoo; Jae-Yoo ; et
al. |
March 16, 2006 |
Apparatus and method for controlling operation of compressor
Abstract
An apparatus for controlling an operation of a compressor
includes: a back electromotive force calculator for calculating a
back electromotive force of a compressor based on a value of a
current applied to a motor of the compressor and a value of a
voltage applied to the motor of the compressor; an operation
frequency reference value determining unit for detecting a
mechanical resonance frequency of the compressor based on the back
electromotive force value and the current value and determining the
detected mechanical resonance frequency as an operation frequency
reference value; and a controller for varying an operation
frequency of the compressor according to the determined operation
frequency reference value.
Inventors: |
Yoo; Jae-Yoo; (Gwangmyeong,
KR) ; Lee; Chel-Woong; (Seoul, KR) ; Sung;
Ji-Won; (Seoul, KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
LG Electronics Inc.
|
Family ID: |
36157400 |
Appl. No.: |
11/033281 |
Filed: |
January 12, 2005 |
Current U.S.
Class: |
417/44.11 ;
417/45 |
Current CPC
Class: |
F04B 35/045 20130101;
F04B 2203/0402 20130101; F04B 49/065 20130101; F04B 2203/0401
20130101; F04B 2203/0404 20130101 |
Class at
Publication: |
417/044.11 ;
417/045 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2004 |
KR |
72825/2004 |
Claims
1. An apparatus for controlling an operation of a compressor
comprising: a back electromotive force calculator for calculating a
back electromotive force of a compressor based on a value of a
current applied to a motor of the compressor and a value of a
voltage applied to the motor of the compressor; an operation
frequency reference value determining unit for detecting a
mechanical resonance frequency of the compressor based on the back
electromotive force value and the current value and determining the
detected mechanical resonance frequency as an operation frequency
reference value; and a controller for varying an operation
frequency of the compressor according to the determined operation
frequency reference value.
2. The apparatus of claim 1, wherein the operation frequency
reference value determining unit multiplies back electromotive
force (BEMF) values and current values during one period and
determining an operation frequency when the sum of multiplied
values is the maximum as the operation frequency reference
value.
3. The apparatus of claim 1, wherein the operation frequency when
the sum of the multiplied values is the maximum, the operation
frequency is identical to a mechanical frequency of the
compressor.
4. The apparatus of claim 1, wherein the BEMF is calculated through
equation shown below: BEMF = V M - Ri - L .times. d i d t ,
##EQU3## wherein `R` is a motor resistance value, `L` is a motor
inductance value, V.sub.M is a value of a voltage applied to the
motor, and `i` is a value of a current applied to the motor.
5. The apparatus of claim 1, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is greater than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is greater than a previous operation frequency,
the operation frequency reference value determining unit
continuously increases the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
6. The apparatus of claim 1, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is greater than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is smaller than a previous operation frequency,
the operation frequency reference value determining unit
continuously reduces the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
7. The apparatus of claim 1, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is smaller than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is smaller than a previous operation frequency,
the operation frequency reference value determining unit
continuously increases the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
8. The apparatus of .claim 1, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is smaller than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is greater than a previous operation frequency,
the operation frequency reference value determining unit 80
continuously reduces the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
9. An apparatus for controlling an operation of a compressor
comprising: a current detector for detecting a current applied to a
motor of a compressor; a voltage detector for detecting a voltage
applied to the motor; a stroke calculator for calculating a stroke
estimate value based on the detected current and voltage values and
a parameter of the motor; a back electromotive force calculator for
calculating a back electromotive force based on the voltage value
of the voltage detector and the current value of the current
detector; an operation frequency reference value determining unit
for detecting a mechanical resonance frequency of the compressor
based on the obtained back electromotive force value and the
detected current value and determining the detected mechanical
resonance frequency as an operation frequency reference value; a
comparator for comparing the stroke estimate value outputted from
the stroke calculator with a stroke reference value and outputting
a difference value according to the comparison result; and a
controller for controlling an operation of the compressor by
varying a current operation frequency according to the determined
operation frequency reference value and varying the voltage applied
to the motor of the compressor according to the difference value
outputted from the comparator.
10. The apparatus of claim 9, wherein the operation frequency
reference value determining unit multiplies back electromotive
force (BEMF) values and current values during one period and
determining an operation frequency detected when the sum of
multiplied values is the maximum as the operation frequency
reference value.
11. The apparatus of claim 9, wherein the operation frequency
reference value determining unit multiplies back electromotive
force (BEMF) values and current values during one period,
recognizing an operation frequency detected when the sum of the
multiplied values is the maximum as a mechanical resonance
frequency of the compressor, and determining the mechanical
resonance frequency as the operation frequency reference value.
12. The apparatus of claim 9, wherein the BEMF is calculated
through equation shown below: BEMF = V M - Ri - L .times. d i d t ,
##EQU4## wherein `R` is a motor resistance value, `L` is a motor
inductance value, V.sub.M is a value of a voltage applied to the
motor, and `i` is a value of a current applied to the motor.
13. The apparatus of claim 9, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is greater than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is greater than a previous operation frequency,
the operation frequency reference value determining unit
continuously increases the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
14. The apparatus of claim 13, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is greater than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is smaller than a previous operation frequency,
the operation frequency reference value determining unit
continuously reduces the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
15. The apparatus of claim 14, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is smaller than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is smaller than a previous operation frequency,
the operation frequency reference value determining unit
continuously increases the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
16. The apparatus of claim 15, wherein if the sum of the values
obtained by multiplying the back electromotive force values and the
current values during one period is smaller than the sum of the
values obtained by multiplying the back electromotive force values
and the current values during a previous one period and the current
operation frequency is greater than a previous operation frequency,
the operation frequency reference value determining unit
continuously reduces the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value.
17. A method for controlling an operation of the compressor
comprising: calculating a back electromotive force of a motor based
on a value of a current applied to the motor of a compressor and a
value of a voltage applied to the motor of the compressor;
detecting a mechanical resonance frequency of the compressor based
on the back electromotive force value and the value of the current;
determining the mechanical resonance frequency as an operation
frequency reference value of the compressor; and varying an
operation frequency of the compressor according to the determined
operation frequency reference value.
18. The method of claim 17, wherein the step of determining the
operation frequency reference value comprises: multiplying back
electromotive force values and current values during one period;
adding the multiplied values; and determining the operation
frequency detected when the sum of the multiplied values is the
maximum as the operation frequency reference value.
19. The method of claim 17, wherein, in the step of determining the
operation frequency as the operation frequency reference value, in
order to make the operation frequency of the compressor identical
to the mechanical resonance frequency of the compressor, the
operation frequency detected when the sum of the multiplied values
is the maximum is determined as the operation frequency reference
value.
20. The method of claim 17, wherein the step of determining the
mechanical resonance frequency as the operation frequency reference
value comprises: a step in which if the sum of the values obtained
by multiplying the back electromotive force values and the current
values during one period is greater than the sum of the values
obtained by multiplying the back electromotive force values and the
current values during a previous one period and the current
operation frequency of the compressor is greater than a previous
operation frequency, the current operation frequency is
continuously increased and an operation frequency detected when the
sum of values obtained by multiplying the back electromotive force
values and the current values during a current one period is the
maximum, is determined as an operation frequency reference value; a
step in which if the sum of the values obtained by multiplying the
back electromotive force values and the current values during one
period is greater than the sum of the values obtained by
multiplying the back electromotive force values and the current
values during a previous one period and the current operation
frequency is smaller than a previous operation frequency, the
current operation frequency is continuously reduced and an
operation frequency detected when the sum of values obtained by
multiplying the back electromotive force values and the current
values during a current one period is the maximum, is determined as
an operation frequency reference value; a step in which if the sum
of the values obtained by multiplying the back electromotive force
values and the current values during one period is smaller than the
sum of the values obtained by multiplying the back electromotive
force values and the current values during a previous one period
and the current operation frequency is smaller than a previous
operation frequency, the current operation frequency is
continuously increased and an operation frequency detected when the
sum of values obtained by multiplying the back electromotive force
values and the current values during a current one period is the
maximum, is determined as an operation frequency reference value;
and a step in which if the sum of the values obtained by
multiplying the back electromotive force values and the current
values during one period is smaller than the sum of the values
obtained by multiplying the back electromotive force values and the
current values during a previous one period and the current
operation frequency is greater than a previous operation frequency,
the current operation frequency is continuously reduced and an
operation frequency detected when the sum of values obtained by
multiplying the back electromotive force values and the current
values during a current one period is the maximum, is determined as
an operation frequency reference value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a compressor and, more
particularly, to an apparatus and method for controlling an
operation of a reciprocating compressor.
[0003] 2. Description of the Prior Art
[0004] In general, a reciprocating compressor does not employ a
crank shaft for converting a rotational motion to a linear motion,
so it has higher compression efficiency than a general
compressor.
[0005] When the reciprocating compressor is used for a refrigerator
or an air-conditioner, a compression ratio of the reciprocating
compressor can be varied by varying a stroke voltage inputted to
the reciprocating compressor in order to control cooling
capacity.
[0006] A conventional reciprocating compressor will now be
described with reference to FIG. 1.
[0007] FIG. 1 is a block diagram showing the construction of an
apparatus for controlling an operation of a reciprocating
compressor in accordance with a prior art.
[0008] As shown in FIG. 1, a conventional apparatus for controlling
an operation of a reciprocating compressor includes: a current
detector 4 for detecting a current applied to a motor (not shown)
of a reciprocating compressor 6; a voltage detector 3 for detecting
a voltage applied to the motor; a stroke calculator 5 for
calculating a stroke estimate value of the compressor based on the
detected current and voltage values and a parameter of the motor; a
comparator 1 for comparing the calculated stroke estimate value and
a pre-set stroke reference value and outputting a different value
according to the comparison result; and a stroke controller 2 for
controlling an operation (stroke) of the compressor 6 by varying a
voltage applied to the motor according to the difference value.
[0009] The apparatus for controlling an operation of the
reciprocating compressor operates as follows.
[0010] First, the current detector 4 detects a current applied to
the motor of the compressor 6 and outputs the detected current
value to the stroke calculator 5. At this time, the voltage
detector 3 detects a voltage applied to the motor and outputs the
detected voltage value to the stroke calculator 5.
[0011] The stroke calculator 5 calculates a stroke estimate value
(X) of the compressor by substituting the detected current and
voltage values and a parameter of the motor to equation (1) shown
below and applies the obtained stroke estimate value (X) to the
comparator 1. X = 1 .alpha. .times. .intg. ( V M - Ri - L .times. i
_ ) .times. d t ( 1 ) ##EQU1## wherein `R` is a motor resistance
value, `L` is a motor inductance value, a is a motor constant
value, V.sub.M is a value of a voltage applied to the motor, `i` is
a value of a current applied to the motor, and `{overscore (i)}` is
a time change rate of the current applied to the motor. Namely,
`{overscore (i)}` is a differentiated value of `i` (di/dt).
[0012] The comparator 1 compares the stroke estimate value with the
stroke reference value and applies a difference value according to
the comparison result to the stroke controller 2.
[0013] The stroke controller 2 controls the stroke of the
compressor 6 by varying a voltage applied to the motor of the
compressor 6 based on the difference value. This will be described
with reference to FIG. 2.
[0014] FIG. 2 is a flow chart of a method for controlling an
operation of the reciprocating compressor in accordance with the
prior art.
[0015] First, when the stroke calculate 5 applies the stroke
estimate value to the comparator 1 (step S1), the comparator 1
compares the stroke estimate value with the pre-set stroke
reference value (step S2) and outputs a difference value according
to the comparison result to the stroke controller 2.
[0016] If the stroke estimate value is smaller than the stroke
reference value, the stroke controller 2 increases a voltage
applied to the motor to control the stroke of the compressor (step
S3). If, however, the stroke estimate value is greater than the
stroke reference value, the stroke controller 2 reduces the voltage
applied to the motor (step S4).
[0017] Thus, in the conventional apparatus and method for
controlling an operation of the reciprocating compressor, even
though a mechanical resonance frequency of the compressor is varied
because of the change in the voltage applied to the motor of the
compressor based on the stroke estimate value an the stroke
reference value, the reciprocating compressor is operated with the
always same operation frequency, causing a problem that operation
efficiency of the reciprocating compressor deteriorates.
[0018] A reciprocating compressor in accordance with a different
embodiment of the present invention is disclosed in U.S. Pat. No.
6,644,943 issued on Nov. 11, 2003.
SUMMARY OF THE INVENTION
[0019] Therefore, an object of the present invention is to provide
an apparatus and method for controlling an operation of a
compressor capable of enhancing operation efficiency of a
compressor even though a load of the compressor is changed.
[0020] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described herein, there is provided an apparatus for controlling an
operation of a compressor including: a back electromotive force
calculator for calculating a back electromotive force of a
compressor based on a value of a current applied to a motor of the
compressor and a value of a voltage applied to the motor of the
compressor; an operation frequency reference value determining unit
for detecting a mechanical resonance frequency of the compressor
based on the back electromotive force value and the current value
and determining the detected mechanical resonance frequency as an
operation frequency reference value; and a controller for varying
an operation frequency of the compressor according to the
determined operation frequency reference value.
[0021] To achieve the above object, there is also provided an
apparatus for controlling an operation of a compressor including: a
current detector for detecting a current applied to a motor of a
compressor; a voltage detector for detecting a voltage applied to
the motor; a stroke calculator for calculating a stroke estimate
value based on the detected current and voltage values and a
parameter of the motor; a back electromotive force calculator for
calculating a back electromotive force based on the voltage value
of the voltage detector and the current value of the current
detector; an operation frequency reference value determining unit
for detecting a mechanical resonance frequency of the compressor
based on the obtained back electromotive force value and the
detected current value and determining the detected mechanical
resonance frequency as an operation frequency reference value; a
comparator for comparing the stroke estimate value outputted from
the stroke calculator with a stroke reference value and outputting
a difference value according to the comparison result; and a
controller for controlling an operation of the compressor by
varying a current operation frequency according to the determined
operation frequency reference value and varying the voltage applied
to the motor of the compressor according to the difference value
outputted from the comparator.
[0022] To achieve the above object, there is also provided a method
for controlling an operation of the compressor including:
calculating a back electromotive force of a motor based on a value
of a current applied to the motor of a compressor and a value of a
voltage applied to the motor of the compressor; detecting a
mechanical resonance frequency of the compressor based on the back
electromotive force value and the value of the current; determining
the mechanical resonance frequency as an operation frequency
reference value of the compressor; and varying an operation
frequency of the compressor according to the determined operation
frequency reference value.
[0023] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0025] In the drawings:
[0026] FIG. 1 is a block diagram showing the construction of an
apparatus for controlling an operation of a reciprocating
compressor in accordance with a prior art;
[0027] FIG. 2 is a flow chart of a method for controlling the
operation of the reciprocating compressor in accordance with the
prior art;
[0028] FIG. 3 is a block diagram showing the construction of an
apparatus for controlling an operation of a reciprocating
compressor in accordance with the present invention;
[0029] FIGS. 4A to 4C are graphs showing a phase of a current
applied to a motor of the compressor and a velocity of the motor;
and
[0030] FIG. 5 is a flow chart of a method for controlling the
operation of the reciprocating compressor in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] An apparatus and method for controlling an operation of a
compressor capable of enhancing operation efficiency of a
compressor even though a load of a compressor is changed by
detecting a mechanical resonance frequency of the compressor based
on a back electromotive force value and a current value of the
compressor and varying an operation frequency of the compressor
according to the mechanical resonance frequency, in accordance with
a preferred embodiment of the present invention will now be
described with reference to FIGS. 3 to 5.
[0032] FIG. 3 is a block diagram showing the construction of an
apparatus for controlling an operation of a reciprocating
compressor in accordance with the present invention.
[0033] As shown in FIG. 3, the apparatus for controlling an
operation of a reciprocating compressor in accordance with the
present invention includes: a current detector 40 for detecting a
current applied to a motor (not shown) of a compressor 60; a
voltage detector 30 for detecting a voltage applied to the motor of
the compressor; a stroke calculator 50 for calculating a stroke
estimate value of the compressor 60 based on the detected current
and voltage values and a parameter of the motor; a back
electromotive force calculator 70 for calculating a back
electromotive force based on the voltage value of the voltage
detector 30 and the current value of the current detector 40; an
operation frequency reference value determining unit 80 for
detecting a mechanical resonance frequency of the compressor based
on the calculated back electromotive force value and the detected
current value and determining the detected mechanical resonance
frequency as an operation frequency reference value; a comparator
10 for comparing the stroke estimate value outputted from the
stroke calculator 50 with a stroke reference value and outputting a
difference value according to the comparison result; and a
controller 20 for controlling an operation of the compressor 60 by
varying a current operation frequency according to the determined
operation frequency reference value and varying a voltage applied
to the motor of the compressor 60 according to the difference value
outputted from the comparator 10.
[0034] The operation of the apparatus for controlling an operation
of the compressor in accordance with the present invention will be
described as follows.
[0035] First, the current detector 40 detects a current applied to
the compressor 60 and outputs the detected current value to the
stroke calculator 50, the back electromotive force calculator 70
and the operation frequency reference value determining unit 80. At
this time, the voltage detector 30 detects a voltage applied to the
compressor 60 and outputs the detected voltage to the stroke
calculator 50 and the back electromotive calculator 70.
[0036] The stroke calculator 50 calculates a stroke estimate value
of the compressor 60 based on the current value outputted from the
current detector 10, the voltage value outputted from the voltage
detector 20 and the pre-set parameter of the motor, and then,
outputs the calculated stroke estimate value to the comparator
10.
[0037] The comparator 10 compares the stroke reference value with
the stroke estimate value outputted from the stroke calculator 50,
and outputs the difference value according to the comparison result
to the controller 20.
[0038] The controller 20 controls a stroke of the compressor by
varying the voltage applied to the compressor 60 according to the
difference value outputted from the comparator 10.
[0039] Meanwhile, the back electromotive force calculator 70
calculates a back electromotive force (BEMF) of the compressor 60
based on the voltage value detected by the voltage detector 30 and
the current value detected by the current detector 40. Preferably,
the BEMF is calculated through equation (2) shown below: BEMF = V M
- Ri - L .times. d i d t ( 2 ) ##EQU2## wherein `R` is a motor
resistance value, `L` is a motor inductance value, V.sub.M is a
value of a voltage applied to the motor and `i` is a value of a
current applied to the motor.
[0040] The operation frequency reference value determining unit 80
detects a mechanical resonance frequency of the compressor based on
the BEMF value and the current value, and determines the detected
mechanical resonance frequency as an operation frequency reference
value. For example, when the motor is in the resonant state, all of
the values obtained by multiplying values of BEMF during one period
and the detected current values have a positive (+) value, so that
the sum of the multiplied values is a maximum value. Namely, when
the sum of values obtained by multiplying the BEMF values of the
motor and the detected current values is the maximum value, the
operation frequency becomes equivalent to the mechanical resonance
frequency.
[0041] Accordingly, the operation frequency reference value
determining unit 80 recognizes an operation frequency detected when
the sum of values obtained by multiplying the BEMF values and the
detected current values is the maximum value as a mechanical
resonance frequency, and determines the mechanical resonance
frequency as the operation frequency reference value. Herein, when
the operation frequency and the mechanical resonance frequency are
identical, operation efficiency of the compressor is enhanced.
[0042] The mechanical resonance frequency value can be detected
through equation (3) shown below: .SIGMA.(BEMF.times.i) (3)
[0043] That is, the operation frequency reference value determining
unit 80 recognizes the operation frequency obtained when a value
calculated through equation (3) is the maximum as the mechanical
resonance frequency and determines the recognized mechanical
resonance frequency as the operation frequency reference value.
Herein, the BEMF is a back electromotive force and `i` is a value
of a current applied to the motor.
[0044] Thereafter, the controller 20 controls an operation of the
compressor 60 by varying a current operation frequency of the
compressor 60 according to the operation frequency reference value
outputted from the operation frequency reference value determining
unit 80. Namely, if the operation frequency reference value is
greater than the current operation frequency value, the controller
increases the current operation frequency, whereas if the operation
frequency reference value is smaller than the current operation
frequency value, the controller reduces the current operation
frequency.
[0045] FIGS. 4A to 4C are graphs showing a phase of a current
applied to a motor of the compressor and a velocity of the motor,
namely, showing states of the mechanical resonance frequency and
the operation frequency when the sum of values obtained by
multiplying the velocity values and current values during one
period is the maximum or not.
[0046] As shown in FIGS. 4A to 4C, in the present invention, it was
revealed through experimentation that even though a load of the
compressor is changed, when the sum of values obtained by
multiplying the back electromotive force values of the motor and
values of a current applied to the motor is maximum, a resonance
phenomenon occurs.
[0047] Herein, the reason why the current values and the velocity
values during one period are multiplied, not that the current
values and the back electromotive force values during one period
are multiplied, is because the back electromotive force generated
from the motor is in proportion to the velocity, so the velocity
phase and the current phase of the motor are shown in graphs and
the current values and the velocity values are multiplied. In other
words, in principle, if the mechanical resonance frequency is the
same as the operation frequency, the phase of the current and the
phase of the velocity becomes the same. At this time, when the sum
of the values obtained by multiplying the current values and the
velocity values is the maximum, the phase of the current and the
phase of the velocity are equal to each other.
[0048] FIG. 4A is a graph showing that a phase of a current applied
to the motor of the compressor and a phase of a velocity of the
motor are the same and a mechanical resonance frequency and an
operation frequency are the same.
[0049] As shown in FIG. 4A, when the phase of the current and the
phase of the velocity are the same, values obtained by multiplying
the current values and the velocity values during one period have
only the positive (+) values, so that the sum of the values
obtained by multiplying the current values and the velocity values
is the maximum.
[0050] FIG. 4B is a graph showing that a phase of the current
applied to the motor of the compressor leads a phase of the
velocity of the motor and an operation frequency is greater than a
mechanical resonance frequency.
[0051] As shown in FIG. 4B, when the phase of the current applied
to the motor of the compressor leads the phase of the velocity of
the motor, the values obtained by multiplying current values and
velocity values during one period have the negative (-) value and
the positive (+) value. Accordingly, the sum of values obtained by
multiplying the current values and the velocity values in the case
that the phase of the current leads the phase of the velocity, is
smaller than the sum of values obtained by multiplying the current
values and the velocity values in the case that the phase of the
current and the phase of the velocity are the same.
[0052] FIG. 4C is a graph showing that the phase of the current
applied to the motor of the compressor lags behind the phase of the
velocity and the operation frequency is smaller than the mechanical
resonance frequency.
[0053] As shown in FIG. 4C, when the phase of the current lags
behind the phase of the velocity, the values obtained by
multiplying current values and velocity values during one period
have a negative (-) value and positive (+) value. Accordingly, the
sum of values obtained by multiplying the current values and the
velocity values in the case that the phase of the current lags
behind the phase of the velocity is smaller than the sum of values
obtained by multiplying the current values and the velocity values
in the case that the phase of the current and the phase of the
velocity are the same.
[0054] The operation of the operation frequency reference value
determining unit 80 for multiplying the back electromotive force
values and the current values during one period, adding the
multiplied values, detecting an operation frequency when the sum is
the maximum value, and determining the detected operation frequency
value as an operation frequency reference value, will now be
described in detail with reference to FIG. 5.
[0055] FIG. 5 is a flow chart of a method for controlling the
operation of the reciprocating compressor in accordance with the
present invention.
[0056] As shown in FIG. 5, the method for controlling an operation
of the compressor in accordance with the present invention
includes: detecting a value of a current and a value of a voltage
applied to the compressor 60; calculating a back electromotive
force of the compressor based on the current and voltage values;
detecting a mechanical resonance frequency of the compressor based
on the sum of values obtained by multiplying back electromotive
force values and current values during one period and determining
the mechanical resonance frequency as an operation frequency
reference value; and varying a current operation frequency of the
compressor based on the determined operation frequency reference
value.
[0057] The operation frequency in case that the sum of values
obtained by multiplying the back electromotive force values and the
current values during one period is the maximum is identical to the
mechanical resonance frequency of the compressor. Accordingly, when
a current operation frequency is varied according to the operation
frequency in the case that the sum of values obtained by
multiplying the back electromotive force values and the current
values during one period is the maximum, the varied operation
frequency becomes identical to the mechanical resonance frequency,
and thus, operation efficiency of the compressor can be
enhanced.
[0058] First, the operation frequency reference value determining
unit 80 calculates the sum of values obtained by multiplying the
back electromotive force values and the current values during one
period (step S11) and compares the calculated sum with the sum of
values obtained by multiplying back electromotive force values and
current values during a previous one period (step S12).
[0059] If the sum of the values obtained by multiplying the back
electromotive force values and the current values during one period
is greater than the sum of the values obtained by multiplying the
back electromotive force values and the current values during a
previous one period and the current operation frequency of the
compressor 60 is greater than a previous operation frequency, the
operation frequency reference value determining unit 80
continuously increases the current operation frequency and then
determines an operation frequency (identical to the mechanical
resonance frequency) when the sum of values obtained by multiplying
the back electromotive force values and the current values during
one period is the maximum as an operation frequency reference value
(steps S13 and S15).
[0060] If the sum of the values obtained by multiplying the back
electromotive force values and the current values during one period
is greater than the sum of the values obtained by multiplying the
back electromotive force values and the current values during a
previous one period and the current operation frequency of the
compressor 60 is smaller than a previous operation frequency, the
operation frequency reference value determining unit 80
continuously reduces the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value (steps S13 and S16).
[0061] If the sum of the values obtained by multiplying the back
electromotive force values and the current values during one period
is smaller than the sum of the values obtained by multiplying the
back electromotive force values and the current values during a
previous one period and the current operation frequency of the
compressor 60 is smaller than a previous operation frequency, the
operation frequency reference value determining unit 80
continuously increases the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value (steps S14 and S17).
[0062] If the sum of the values obtained by multiplying the back
electromotive force values and the current values during one period
is smaller than the sum of the values obtained by multiplying the
back electromotive force values and the current values during a
previous one period and the current operation frequency of the
compressor 60 is greater than a previous operation frequency, the
operation frequency reference value determining unit 80
continuously reduces the current operation frequency and then
determines an operation frequency when the sum of values obtained
by multiplying the back electromotive force values and the current
values during a current one period is the maximum as an operation
frequency reference value (steps S14 and S18).
[0063] Therefore, the operation frequency when the sum of the
values obtained by multiplying the back electromotive force values
and the current values during one period is the maximum is
identical to the mechanical resonance frequency of the compressor,
so that operation efficiency of the compressor can be enhanced by
varying the current operation frequency according to the operation
frequency when the sum of the values obtained by multiplying the
back electromotive force values and the current values during one
period.
[0064] In other words, while the reciprocating compressor is
operating, whenever a load of the compressor is varied, a
mechanical resonance frequency of the compressor is detected based
on the back electromotive force values and the current values
during one period and then the operation frequency of the
compressor is varied according to the detected mechanical resonance
frequency, whereby the operation efficiency of the compressor can
be enhanced.
[0065] As so far described, the apparatus and method for
controlling an operation of a reciprocating compressor in
accordance with the present invention has the following
advantages.
[0066] That is, whenever a load of the compressor is varied, a
mechanical resonance frequency of the compressor is detected based
on back electromotive force values and current values during one
period and an operation frequency of the compressor is varied
according to the detected mechanical resonance frequency.
Accordingly, even when the load of the compressor is varied,
operation efficiency of the compressor can be enhanced.
[0067] As the present invention may be embodied in several forms
without departing from the spirit or essential characteristics
thereof, it should also be understood that the above-described
embodiments are not limited by any of the details of the foregoing
description, unless otherwise specified, but rather should be
construed broadly within its spirit and scope as defined in the
appended claims, and therefore all changes and modifications that
fall within the metes and bounds of the claims, or equivalence of
such metes and bounds are therefore intended to be embraced by the
appended claims.
* * * * *